Databases and Collections in MongoDB

MongoDB stores data records as documents (specifically BSON documents) which are gathered together in collections. A database stores one or more collections of documents.

You can manage databases and collections on the Atlas cluster from the Atlas UI, mongosh, or MongoDB Compass. This page describes how to manage databases and collections on the Atlas cluster from the Atlas UI. For self-managed deployments, you can use mongosh or MongoDB Compass to manage databases and collections.

Select the client that you want to use to manage databases and collections.

Atlas UI

MongoDB Atlas is a multi-cloud database service that simplifies deploying and managing your databases on the cloud providers of your choice.

mongosh

The MongoDB Shell, mongosh, is a JavaScript and Node.js REPL (Read Eval Print Loop) environment for interacting with MongoDB deployments. To learn more, see mongosh.

MongoDB Compass

MongoDB Compass is a powerful GUI for querying, aggregating, and analyzing your MongoDB data in a visual environment. To learn more, see MongoDB Compass.

Databases

In MongoDB, databases hold one or more collections of documents.

Atlas UI

To select a database to use, log in to Atlas and go to the Data Explorer page for your project.

Select your organization and project

• If it’s not already displayed, select the organization that contains your project from the Organizations menu in the navigation bar.

• If it’s not already displayed, select your project from the Projects menu in the navigation bar.

Open the Data Explorer

In the sidebar, click Data Explorer under the Database heading.

The Data Explorer displays.

mongosh

To select a database to use, in mongosh, issue the use <db> statement, as in the following example:

use myDB

MongoDB Compass

To select a database to use, complete the following steps:

Start MongoDB Compass and connect to your cluster.

To learn more, see Connect to MongoDB.

Select Databases from the left navigation.

The Databases tab opens to list the existing databases for your MongoDB deployment.

Create a Database

Atlas UI

To create a new database in Atlas, perform the following steps:

1. If it’s not already displayed, select the organization that contains your project from the Organizations menu in the navigation bar. Select your project from the Projects menu. In the sidebar, click Data Explorer under the Database heading. The Data Explorer displays.

2. In the Connections sidebar, select or hover over your cluster and click the icon to open the Create Database dialog box.

3. Enter the Database Name and the Collection Name

   Enter the Database Name and the Collection Name to create the database and its first collection.

   If you want to use custom collation on the collection, select the Use Custom Collation checkbox and select the desired collation settings.

   Don’t include sensitive information in your database and collection names.

   For more information on MongoDB database names and collection names, see Naming Restrictions.

4. Select whether the collection is a time series collection. If you select to create a time series collection, specify the time field and granularity. You can optionally specify the meta field and the time for old data in the collection to expire.

5. Upon successful creation, the database and the collection appears in the Connections sidebar.

mongosh

If a database does not exist, MongoDB creates the database when you first store data for that database. As such, you can switch to a non-existent database and perform the following operation in mongosh:

use myNewDB

db.myNewCollection1.insertOne( { x: 1 } )

The insertOne() operation creates both the database myNewDB and the collection myNewCollection1 if they do not already exist. Be sure that both the database and collection names follow MongoDB Naming Restrictions.

MongoDB Compass

Open the Databases tab.

Click the Create database button.

Enter database and first collection names in the Create Database dialog.

Click Create Database to create the database and its first collection.

Collections

MongoDB stores documents in collections. Collections are analogous to tables in relational databases.

Create a Collection

If a collection does not exist, MongoDB creates the collection when you first store data for that collection.

Atlas

To create a new collection in Atlas, perform the following steps:

1. If it’s not already displayed, select the organization that contains your project from the Organizations menu in the navigation bar. Select your project from the Projects menu. In the sidebar, click Data Explorer under the Database heading. The Data Explorer displays.

2. Select or hover over the database, and click the icon to open the Create Collection dialog box.

3. In the Create Collection dialog box, enter the name of the collection you want to create.

   Atlas also provides Additional preferences. You can choose from the following options:

   • Create a Clustered Collection

   • Create a Collection with Collation

   Don’t include sensitive information in your collection name.

   For more information on MongoDB collection names, see Naming Restrictions.

4. Select whether the collection is a time series collection. If you select to create a time series collection, specify the time field and granularity. You can optionally specify the meta field and the time for old data in the collection to expire.

5. Upon successful creation, the collection appears underneath the database in the Connections sidebar.

mongosh

db.myNewCollection2.insertOne( { x: 1 } )
db.myNewCollection3.createIndex( { y: 1 } )

Both the insertOne() and the createIndex() operations create their respective collection if they do not already exist. Be sure that the collection name follows MongoDB Naming Restrictions.

MongoDB Compass

Click the name of the database where you to want to create a collection in the left navigation.

Click the + icon next to the database name.

Enter the name of the collection in the Create Collection dialog.

Click Create Collection to create the collection.

Atlas

mongosh

Explicit Creation

MongoDB provides the db.createCollection() method to explicitly create a collection with various options, such as setting the maximum size or the documentation validation rules. If you are not specifying these options, you do not need to explicitly create the collection since MongoDB creates new collections when you first store data for the collections.

To modify these collection options, see collMod.

MongoDB Compass

Explicit Creation

Click the name of the database where you to want to create a collection in the left navigation.

Click the Create collection button.

Enter the name of the collection and optionally, configure additional preferences.

Click Create Collection to create the collection.

MongoDB Compass provides the following additional preferences that you can configure for your collection:

• Create a Capped Collection

• Create a Clustered Collection

• Create a Collection with Collation

• Create a Collection with Encrypted Field

• Create a Time Series Collection

Schema Validation

By default, a collection does not require its documents to have the same schema; i.e. the documents in a single collection do not need to have the same set of fields and the data type for a field can differ across documents within a collection.

However, you can enforce schema validation rules for a collection during update and insert operations. See Schema Validation for details.

For deployments hosted in MongoDB Atlas, the Performance Advisor and the MongoDB Atlas UI detect common schema design issues and suggest modifications that follow MongoDB best practices. To learn more, see Schema Suggestions.

Modifying Document Structure

To change the structure of the documents in a collection, such as add new fields, remove existing fields, or change the field values to a new type, update the documents to the new structure.

Unique Identifiers

Collections are assigned an immutable UUID (Universally unique identifier). The collection UUID remains the same across all members of a replica set and shards in a sharded cluster.

Atlas

mongosh

To retrieve the UUID for a collection, run either the listCollections command or the db.getCollectionInfos() method.

MongoDB Compass